Evolutionary Evidence
An organism has chlorophyll a and b, cellulose walls, and stores starch in chloroplasts. Which conclusion is justified?
A. It must be an angiosperm.
B. It must be a land plant.
C. It could be a green alga or a land plant.
D. It must have vascular tissue.
C
The listed traits occur in both green algae and land plants.
A fern spore develops into an egg-producing organism. Which sequence is correct?
A. n spore → mitosis → n gametophyte
B. n spore → meiosis → n gametophyte
C. 2n spore → meiosis → n sporophyte
D. n spore → fertilization → 2n gametophyte
A
A haploid spore grows into a haploid gametophyte by mitosis.
A thicker cuticle evolves without an effective route for gas exchange. What is the most likely tradeoff?
A. Increased water loss and increased CO₂ uptake
B. Decreased water loss and increased CO₂ uptake
C. Decreased water loss and decreased CO₂ uptake
D. Increased water loss and decreased CO₂ uptake
C
The barrier conserves water but restricts CO₂ entry.
Compatible pollen lands on a flower’s stigma, but a treatment prevents pollen-tube growth. Has pollination occurred? Has fertilization occurred? Identify the blocked connection between them.
Pollination has occurred; fertilization has not. Pollen reached the stigma, but sperm cannot be delivered through the pollen tube to the female gametophyte within an ovule.
A plant has inconspicuous flowers without showy petals. A student concludes that it cannot reproduce sexually because it cannot attract animal pollinators. Identify two flaws in the argument.
First, pollen can be transported by wind, so animal attraction is not required for all flowering plants. Second, petals are not the structures that produce pollen or ovules; stamens and carpels perform those functions. Inconspicuous flowers can retain functional reproductive organs.
Classify each specimen into the most specific major plant group supported by the evidence:
A: Vascular tissue; a large, long-lived sporophyte; an independent gametophyte; sperm that require surface water to reach eggs.
B: Pollen and seeds produced in cones; no flowers or fruits.
C: Seeds enclosed within structures that develop from flower ovaries.
A: Seedless vascular plant, such as a fern. Vascular tissue plus the independent gametophyte and water-dependent fertilization match its life cycle.
B: Gymnosperm. Seeds and pollen in cones, without flowers or fruits, distinguish it here.
C: Angiosperm. Seeds enclosed in ovary-derived fruits are decisive.
A fern sporophyte has 2n = 24. How many chromosomes occur in each of the following?
1. A spore
2. A gametophyte cell
3. A sperm cell
4. A newly formed zygote
Which events change the chromosome-set number?
1. Spore: 12
2. Gametophyte cell: 12
3. Sperm: 12
4. Zygote: 24
Meiosis reduces the set number from 2n to n; fertilization restores it from n to 2n. Mitosis maintains it.
In an otherwise healthy plant:
- Treatment A selectively blocks xylem transport.
- Treatment B selectively blocks phloem transport.
Which treatment most directly limits water delivery to leaves? Which most directly limits delivery of sugars from mature leaves to growing roots? Explain why “phloem always transports downward” is incorrect.
A limits water delivery to leaves. B limits sugar delivery from mature leaves to roots.
Phloem moves sugars from sources to sinks, rather than in one fixed direction. A growing shoot can also be a sink, so sugar transport can occur upward.
Which sequence correctly describes male development in an angiosperm?
A. Microspore → meiosis → pollen → fertilization → sperm
B. Sperm → mitosis → microspore → meiosis → pollen
C. Microspore mother cell → mitosis → pollen → meiosis → sperm
D. Microspore mother cell → meiosis → microspore → mitosis → male gametophyte
D
Meiosis produces microspores; mitosis develops the male gametophyte.
A flower’s stamens are removed before pollen release. How could it still produce seeds sexually?
A. Its petals could produce replacement sperm.
B. Its ovary could develop directly into embryos.
C. Compatible pollen from another flower could reach its stigma.
D. Its ovules could produce pollen through meiosis.
C
Removing stamens leaves functional female structures available for cross-pollination.
Why are ferns more closely related to flowering plants than to mosses?
A. Ferns and flowering plants both produce seeds.
B. They share a more recent common ancestor.
C. Mosses evolved from ferns.
D. Their gametophytes are dominant.
B
Relatedness depends on the most recent common ancestor.
A treatment blocks meiosis but leaves mitosis unaffected. Which process can still occur?
A. New spores form in a fern sporangium.
B. A sporophyte produces haploid spores.
C. A diploid spore mother cell produces normal haploid products.
D. An existing gametophyte produces sperm.
D
Gametophytes produce gametes by mitosis.
A fern survives in moist soil but cannot achieve fertilization when its gametophytes lack a surface water film. Why?
A. Vascular tissue cannot transport water without rain.
B. Its sperm require external water to reach eggs.
C. Meiosis requires sperm to swim.
D. Its spores cannot form without fertilization.
B
Internal water transport does not replace the external film needed by fern sperm.
An angiosperm has 2n = 18. Give the chromosome number and developmental origin of each structure:
1. Embryo
2. Endosperm
3. Seed coat
4. Fruit wall
Embryo: 18; zygote formed by sperm-egg fusion
Endosperm: 27; sperm fusion with the central cell containing two haploid polar nuclei
Seed coat: maternal ovule integuments
Fruit wall: maternal ovary wall
Researchers examine two treated flowers:
Flower A: Pollen reaches the stigma, but no pollen tube reaches an ovule.
Flower B: A pollen tube delivers two sperm; one fertilizes the egg, but the other fails to fuse with the central cell.
For each flower, identify the successful reproductive step and the failed step. Which flower can initiate an embryo? Which lacks normal endosperm formation?
A: Pollination succeeds; sperm delivery and fertilization fail. It cannot initiate an embryo through the normal sexual pathway.
B: Pollination, sperm delivery, and egg fertilization succeed. An embryo can begin developing, but central-cell fertilization fails, so normal endosperm formation does not occur.
Begin with the simplified branching order in the lecture: charophytes outside land plants; nonvascular plants branching before vascular plants; seedless vascular plants branching before seed plants; gymnosperms and angiosperms within seed plants.
Place these innovations at the earliest appropriate branches:
1. Apical meristems and plant-type alternation of generations
2. Vascular tissue
3. Seeds and pollen
4. Flowers and fruits
1. At the origin of land plants, after divergence from charophytes.
2. At the common ancestor of vascular plants.
3. At the common ancestor of gymnosperms and angiosperms.
4. On the angiosperm branch.
A fern has 2n = 24. Which sequence gives the chromosome numbers in a spore, gametophyte cell, sperm, and zygote?
A. 12 → 24 → 12 → 24
B. 12 → 12 → 12 → 24
C. 24 → 12 → 12 → 24
D. 12 → 12 → 6 → 12
B
Meiosis halves chromosome number; fertilization restores it.
Two hypothetical plant lineages possess different innovations:
1. Lineage A has protected embryos, stored food, and dormancy, but its sperm must still swim through external water to reach eggs.
2. Lineage B transfers male gametophytes through air and delivers sperm without external water, but its offspring lack a protected package with stored food and dormancy.
Which lineage has solved the fertilization problem associated with dry land? Which has improved offspring survival through unfavorable periods? Match each solution to the relevant seed-plant innovation.
Lineage B has solved the external-water problem for fertilization through the function associated with pollen and sperm delivery.
Lineage A has improved offspring protection and survival through unfavorable periods through the functions associated with seeds.
Pollen addresses delivery of the male gametophyte and sperm; seeds package and protect the developing sporophyte and support establishment.
An AA flowering plant receives pollen from an aa plant. What are the embryo, endosperm, and seed-coat genotypes, respectively?
A. Aa, AAa, AA
B. Aa, Aaa, Aa
C. AA, AAa, Aa
D. Aa, Aa, AA
A
Embryo is biparental; endosperm has two maternal sets; seed coat is maternal.
Researchers compare two otherwise similar plant populations. Both produce equally viable seeds. Population A produces fleshy fruits eaten by birds; population B produces fruits that birds do not eat.
More seedlings from A establish far from their parent plants. Does this demonstrate that birds increased pollination? Explain what the result supports, and identify a measurement needed to test an effect on pollination.
No. The result supports a role for birds in seed dispersal and subsequent establishment, rather than demonstrating increased pollen transfer.
To test pollination, researchers could compare delivery of compatible pollen to stigmas under controlled bird-access and bird-exclusion conditions before fruit formation. Observing distant seedlings addresses a later stage of reproduction.
Which grouping requires the fewest evolutionary changes to explain the distribution of vascular tissue and seeds?
A. Moss + fern, because both lack seeds
B. Fern + pine, excluding sunflower
C. Moss + sunflower, because both produce embryos
D. Pine + sunflower, with fern as their closest listed outgroup
D
One origin of vascular tissue groups fern with seed plants; one origin of seeds groups pine with sunflower
A moss’s haploid female gametophyte is fertilized by sperm from another gametophyte. A sporophyte grows attached to the female gametophyte and later produces spores.
Identify the generation and ploidy of:
1. The supporting female plant
2. The attached spore-producing structure
3. A released spore
4. The multicellular plant that develops from that spore
Which of these contain a nuclear contribution from the sperm donor, and why is the attached sporophyte not simply a new branch of the female gametophyte?
1. Supporting female plant: gametophyte, n
2. Attached structure: sporophyte, 2n
3. Spore: n
4. Plant developing from the spore: gametophyte, n
The sporophyte contains nuclear contributions from both parents. Its meiotic spores, and the gametophytes developing from them, inherit genetic material through that biparental sporophyte. The original female gametophyte does not gain paternal nuclear DNA from fertilization.
The attached sporophyte begins as a fertilized egg and is diploid. A branch of the female gametophyte would arise through mitosis and remain haploid.
Healthy moss, fern, and pine plants lack external water films. Pine receives compatible pollen. Which outcome is best predicted?
A. Only pine can achieve fertilization.
B. Fern and pine can achieve fertilization because both have xylem.
C. All three can achieve fertilization because their tissues contain water.
D. None can achieve fertilization because all plant sperm must swim externally.
A
Pine’s pollen-associated sperm delivery avoids dependence on an external water film.
In a hypothetical angiosperm, both sperm are normal and haploid. However, the central cell contains only one haploid polar nucleus, rather than the usual two. The egg is normal.
If both fusion events occur:
1. What is the embryo’s ploidy?
2. What is the ploidy of the tissue initiated by sperm–central-cell fusion?
1. Embryo: 2n, from n sperm + n egg.
2. Central-cell fertilization product: 2n, from n sperm + one n polar nucleus.
Bird access increases distant seedling establishment but does not change pollen delivery. Which conclusion is best supported?
A. Birds increased fertilization success.
B. Birds aided seed dispersal.
C. Birds increased ovule production.
D. Birds caused flowers to produce more pollen.
B
The measured effect concerns movement and establishment of offspring.